1. Field
The present disclosure relates generally to vehicles and, in particular, to navigation systems for vehicles. Still more particularly, the present disclosure relates to a method and apparatus for providing navigation to vehicles moving relative to each other.
2. Background
Vehicles, such as aircraft, commonly use navigation systems that include global positioning system devices to provide information about the position of the aircraft. With the information about the position of the aircraft, a pilot, autopilot, or other operator may guide the aircraft during various phases of flight such as take-off, climbing, level flight, descending, and landing.
For example, a global positioning system device may be used to provide information to a pilot as to whether the aircraft is turning at desired waypoints along a flight plan. As another example, a global positioning system device also may be used to provide position information to land the aircraft at a desired location.
Aircraft may use these global positioning system devices to identify their position relative to other objects that have fixed positions. For example, when a helicopter lands at an airport, the landing pad for the helicopter has a fixed position on the ground. As a result, the pilot of the helicopter may use the position of the helicopter and information about the location of the landing pad in a mapped database to land as desired.
In some cases, the object may move relative to the vehicle. For example, a helicopter landing on an aircraft carrier or other surface ship is unable to rely only on the position of the helicopter. Instead, the helicopter may also receive information from the surface ship as to the position of the surface ship relative to the helicopter. This information may aid in landing the helicopter on the surface ship.
This type of information may be provided by a navigation system on the helicopter, the surface ship, or both the helicopter and the surface ship. In some cases, a navigation system on both the helicopter and the surface ship may communicate with each other such that the helicopter knows where it is located relative to the surface ship. For example, the operator of the helicopter may want to know with a desired level of accuracy where the center of a helipad is located on the surface ship.
When the two navigation systems communicate with each other, the pilot of the helicopter may provide information needed to know where the location of the helicopter is relative to the helipad with a desired level of accuracy. These navigation systems include global positioning system devices to provide the desired level of accuracy.
These navigation systems communicate with each other over wireless communications links. These wireless communications links, however, may not always be as reliable as desired. In some cases, a temporary loss in communication between the navigation systems may occur. As a result, the helicopter may not receive information identifying the location of the helicopter relative to the surface ship as precisely as desired when a loss of communication occurs temporarily between the navigation system on the helicopter and the navigation system on the surface ship.
Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.